JP2002182466A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device where a uniform thin layer is formed on a toner carrier without using a layer thickness regulating member and the excellent charge performance (electrification) of toner in a two-component developing system is effectively utilized and by which excellent image quality by a one-component contact type developing system is obtained. SOLUTION: This developing device is equipped with a developing container arranged near an image carrier 1 and two-component developer 51 consisting of magnetic carrier and non-magnetic toner inside, the elastic toner carrier 53 arranged in contact with the image carrier 1, and a developer carrier 55 arranged proximately or in contact with the toner carrier 53. The developer carrier 55 is provided with a magnetic field generation means so as to form a developer brush by the magnetic action of the magnetic field generation means on the developer carrier 55. By applying specified different bias to the toner carrier 53 and the developer carrier 55 and bringing the bristles of the developer brush into contact with the toner carrier, the toner in the developer brush is transferred to the toner carrier 53 so as to form a toner thin layer. Then, by bringing the toner thin layer on the toner carrier 53 into contact with the image carrier 1, an electrostatic latent image on the image carrier 1 is developed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus such as a copying machine or a printer, and more particularly, to a method for forming a uniform thin layer of toner on an elastic toner carrier. The present invention relates to a developing device that develops an electrostatic latent image formed on an image carrier by bringing toner into contact with the surface of the image carrier to visualize the image.

[0002]

2. Description of the Related Art Generally, an image forming apparatus of this type forms an electrostatic latent image on an image carrier such as an electrophotographic photosensitive member, and then develops the electrostatic latent image by providing a developer. Visualize. As the developer, a one-component developer composed of a toner alone or a two-component developer composed of a toner and a carrier carrying the toner is mainly known, and various development systems suitable for them have been developed and proposed. I have.

[0003] Among these systems, there is a contact-type developing device utilizing an elastic developing roller and a non-magnetic toner as one of the noticeable ones. This apparatus uses a conductive (including semiconductive; the same applies hereinafter) elastic developing roller (synonymous with a toner carrier) in contact with an image carrier at a predetermined nip width. A thin toner layer is formed on the surface, and then the toner is pressed against the surface of the image carrier to perform development.

[0004] In such an apparatus, forming a uniform thin layer of toner on the developing roller is one of the important conditions for performing good development, and therefore, various methods are required to form a uniform thin layer. Means have been proposed.

A device using a doctor blade is known as one of the typical devices. In this apparatus, the thickness of the toner passing between the blade and the developing roller is reduced by bringing the tip of the blade into pressure contact with or close to the peripheral surface of the developing roller to form a thin layer. There is a possibility that the accumulation, fusion or fixation of the toner may occur on the inlet side of the leading end, and the pressing force of the blade or the gap between the blade and the developing roller may change, whereby the formation of a uniform thin toner layer may be hindered. Further, the charge amount of the toner varies, and fog and density unevenness easily occur.

In view of this, there has been proposed an apparatus in which a layer thickness regulating roller is disposed in pressure contact with the surface of a developing roller instead of a blade to form a thin layer with toner passing therebetween. In such an apparatus, the layer thickness regulating roller is rotated in a direction opposite to the rotation direction of the developing roller or in a forward direction at a different speed. However, depending on the conditions, the friction between the layer thickness regulating roller and the developing roller becomes considerably high due to contact. In some cases, heat is generated, and the heat locally melts the toner and fuses to the surface of the layer thickness regulating roller or the developing roller.

In particular, with the increase in process speed, 40
There is a tendency to use a toner having a low melting point such as about 80 ° C. (for example, a polymerized toner using a low softening point substance) or a toner having a low glass transition temperature. In some cases, the temperature locally becomes close to or higher than 50 to 60 ° C., and the above-described fusing is likely to occur in a toner having such a low melting point or glass transition temperature.
Such fusion causes streaks and unevenness in the toner layer on the developing roller, hinders good development and adversely affects the durability of image quality.

Further, since the developing roller made of an elastic material such as rubber has a high coefficient of thermal expansion, its diameter tends to change due to a temperature change due to the frictional heat or the like, and the contact nip width between the image carrier and the developing roller is reduced. It may change depending on the temperature and affect the formed image. Further, in the case of a developing roller made of conductive rubber, the electric resistance changes with such a temperature change. For example, in the case of NBR rubber or the like, the one-order resistance changes remarkably with a temperature change of about 20 ° C. Sometimes you do.

Furthermore, in using a non-magnetic one-component toner, it is not sufficient that the toner is charged only by frictional charging of the toner. Therefore, by applying a bias to the above-mentioned layer thickness regulating blade or roller, It is necessary to positively inject and charge the toner in contact therewith.

On the other hand, in an apparatus using this kind of non-magnetic toner, since the toner adheres to the developing roller without using a magnetic attraction force and is exclusively electrostatic, the developing roller is rotated at a high speed. The printer and other devices used have a problem of toner scattering and floating, especially toner leakage from both sides of the developing roller.To prevent such leakage, provide sufficient sealing on both sides of the developing roller. However, if the seal is insufficient, the inside of the device is contaminated with toner.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has a toner layer thickness such as a blade or a roller which tends to affect the durability of image quality as described above with respect to a developing roller. Provided is a developing device which does not require a regulating member and can further suppress leakage of toner from a developing container.

In particular, there is provided a developing device which can effectively utilize good chargeability (charging) of toner in a two-component developing system and can obtain excellent image quality by a one-component contact developing system. .

[0013]

According to the present invention, there is provided a two-component toner comprising a magnetic carrier and a non-magnetic toner disposed in the vicinity of an image carrier capable of forming an electrostatic latent image. A developing container for storing a developer, a conductive and elastic toner carrier disposed in contact with the image carrier and having a predetermined bias applied thereto, and in close proximity to or in contact with the toner carrier. A predetermined bias applied conductive developer carrier having a magnetic field generating means inside or itself, and rotating the developer carrier and the toner carrier to perform development. A developer brush is formed on the developer carrier by the magnetic action of the magnetic field generating means, and the brushes of the brush are brought into contact with the toner carrier to transfer the toner in the developer brush onto the toner carrier, thereby forming a toner. Forming a layer, characterized by developing an electrostatic latent image on the image bearing member by contacting the toner thin layer on the toner carrying member to the image bearing member.

In particular, the developer carrier has a length substantially equal to or longer than the effective electrostatic latent image forming width of the image carrier, and the toner carrier is more centered than the length of the developer carrier. And has a longer length toward both ends.

[0015] In particular, the developer carrier is provided below the toner carrier.

Further, after completion of the developing process, the level of the potential difference between the toner carrier and the developer carrier is temporarily reversed to collect the toner on the toner carrier to the developer carrier side. I do. Further, as one embodied embodiment, the developer carrier may be at a ground potential.

[0017]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of a developing device to which the present invention is applied. In the drawing, reference numeral 1 denotes a photosensitive drum as an image carrier which rotates in a direction indicated by an arrow A, that is, a clockwise direction.
As such an electrophotographic photosensitive member, an organic photosensitive member or an amorphous silicon photosensitive member can be used.

Around the image carrier 1, an eraser lamp 2 for erasing residual charges on the image carrier 1 according to the rotation direction A of the image carrier 1, and a surface of the image carrier 1 after erasing the residual charges Charging device 3 for uniformly charging the image carrier 1 with a specific polarity, an LED head for projecting digital light information on the surface of the uniformly charged image carrier 1 to form an electrostatic latent image on the surface of the image carrier 1, etc. An exposure device 4, a developing device 5 for supplying a powder toner to the surface of the image carrier 1 on which the electrostatic latent image is formed, and converting the electrostatic latent image into a toner image; Transfer material P
A transfer roller 6 as a transfer device for transferring the image onto the image carrier, a cleaner 7 for removing toner remaining on the image carrier 1 after the image transfer, and the like are arranged. Except for the developing device 5, the components around these image carriers may have a known configuration.

The developing device 5 is roughly divided into a developing container 52 which is disposed near the image carrier 1 and contains therein a two-component developer 51 comprising a magnetic carrier and a non-magnetic toner. Conductive and elastic toner carrier 53 arranged so as to be pressed against a predetermined nip width (contact width)
And a conductive developer carrier 55 disposed close to or in contact with the toner carrier 53 and having a magnetic field generator (for example, a magnet roll having S poles and N poles arranged alternately around) therein. And

As shown in the figure, the toner carrier 53 has a roller shape, and is arranged at a position where the line connecting the axis of the toner carrier and the axis of the image carrier 1 is substantially horizontal. The developer carrier 55 has a sleeve shape made of a conductive material, such as aluminum, which is disposed so as to surround the magnetic field generator 54. The axis of the developer carrier 55 is substantially the same as the axis of the toner carrier 53. It is arranged so that it is on the horizontal line. The toner carrier 53 and the developer carrier 55 rotate in directions indicated by arrows B and C, respectively. The toner carrier 53 has a sleeve shape having a magnetic field generating means therein as described above,
3 itself may have a magnetic field generating means, for example, a form of a conductive magnet roll having an S-pole and an N-pole on its peripheral surface in order.

The structure of the toner carrier 53 is described below. The toner carrier 53 is formed around a conductive central axis 53a to which a bias described later is applied.
Is formed, and an elastic surface layer 53c is formed on the outer periphery of the intermediate layer 53b.
Is formed. Although not limited,
For example, the intermediate layer 53b and the surface layer 53c are
Have different electrical properties such that the surface layer 53c has a relatively high electrical resistance and the surface layer 53c has a relatively low electrical resistance. Further, the toner carrier 53 is not limited to the above-described two-layer structure, but may have a single-layer structure, or may have a three- or more-layer structure. As a material of the image carrier 53, in addition to a single layer of silicone rubber, the intermediate layer 53b having a two-layer structure is formed of a porous foam having elasticity such as NBR rubber (acrylonitrile butadiene copolymer rubber) or urethane rubber, and a surface layer. 53c may be an elastic body such as urethane rubber.

For example, as the intermediate layer 53b, 10⁴-10
⁹Ω · cm, 10 as surface layer 53c ⁵-10⁷Ωcm
Volume resistance is preferable, and elasticity is rubber hardness.
Those having a range of about 20 to 40 ° C are preferred.

A stirring / supplying member 56 is provided behind the developer carrying member 55 and close to the developer carrying member 55, and further, a stirring / supplying member 57 is provided in parallel with the stirring / supplying member 56. The stirring and supply members 56 and 57 rotate appropriately during the developing process or at the time of idling to stir and charge (frictionally charge) the developer in the developing container 51 and to transfer the charged developer to the developer carrier 55. To form a developer layer on the surface of the developer carrier 55. The developer layer is provided to the toner carrier 53 by being trimmed by the doctor blade 58 according to the rotation of the developer carrier 55.

A toner hopper 59 is provided so as to be located substantially above the stirring / supplying members 56 and 57. The hopper 59 moves a supply member such as a blade disposed inside along the inner peripheral wall. By rotating the toner, the toner stored therein is sequentially supplied from the lower supply hole 59a to the developing container 52 by a predetermined amount at an appropriate timing.

As described above, an appropriate bias is applied to the toner carrier 53 and the developer carrier 55. For this reason, although not shown, the toner carrier 53 and the developer carrier 55 are connected to an appropriate bias power source, and are provided with biases having different values, that is, on the developer carrier 55 trimmed by the blade 58. A bias having a value such that an optimum potential difference is generated for the transfer is applied so that only the toner component of the developer layer transfers from the developer carrier 55 to the toner carrier 53. The potential difference for obtaining such an optimum transfer can be determined according to other conditions that affect the transfer, such as the amount of charge of the toner.

As described above, the transfer of the toner from the developer carrier 55 to the toner carrier 53 is controlled by the potential difference between them. Therefore, by controlling this potential difference, the thin and uniform toner is deposited on the toner carrier 53. Layers can be formed.

The bias to the toner carrier 53 is
In order to prevent fogging of the toner on the image background portion (background) of the image carrier 1, the absolute value of the surface potential of the image carrier 1 is 100 to 500 V, preferably 300 to 400 V.
V is set to a lower value. As an example, for the image carrier 1 on which an electrostatic latent image having a dark area potential of about -750 V and a light area potential of about -80 V is formed, a volume resistivity of about 3 × 10 ⁶ Ω ·
When a bias of about -400 V was applied to the toner carrying member 53 cm and a bias of about -750 V was applied to the developer carrying member 55, development was performed. Was formed, and the toner image formed on the image carrier 1 was of high quality.

Further, as shown in FIG.
Reference numeral 5 denotes a length substantially equal to the effective electrostatic latent image forming width of the image carrier 1 or a long length.
Reference numeral 3 has a length that is longer toward the both ends around the center than the length of the developer carrier 55. The image carrier 1, the toner carrier 53, and the developer carrier 55 are arranged with their centers substantially aligned. With such an arrangement, the formation of the toner layer on the toner carrier 53 does not extend to both ends thereof, thereby preventing the leakage of toner from both sides of the toner carrier 53 in cooperation with the above-described seal. Can be.

This can be further enhanced by arranging the toner carrier 53 and the developer carrier 55 as shown in FIG. In FIG.
The toner carrier 53 is in pressure contact with the peripheral surface of the image carrier 1 at a position above a horizontal plane including the axis of the image carrier 1, and the developer carrier 55 is located below the toner carrier 53. The toner is supplied to the toner carrier 53 at the position.

When the developing device is arranged vertically, the space for disposing the developing device can be reduced, and the toner falling when the toner carrier 53 rubs the image carrier 1 is located on the lower side. The developer carrier 55 receives and
Further, the toner that leaks from both sides of the toner carrier 53 and the toner that leaks from both sides of the developer carrier 55 can be efficiently collected in the developing container 52.

In addition to the above configuration, after the development process is completed, the bias value applied to the toner carrier 53 and the developer carrier 55 is (temporarily) reversed to reverse the potential difference. As a result, the toner adhering to the toner carrier 53 is once transferred to the developer carrier 55 and collected in the developing container 52, and then when the developing process is started again, the bias value is set to the normal value. The developer may be returned and the fresh toner may be supplied to the toner carrier by the developer carrier 55. By doing so, overcharging and stress of the toner can be eliminated. In addition,
During such recovery, the developer carrier 55 may be set to the ground potential.

[0032]

As described above, according to the present invention, it is possible to form a high-quality image free from fogging and development unevenness by making use of the conventionally known excellent features of the two-component developing system and the one-component developing system. Since the thickness regulating member can be omitted, there is no need to take measures against frictional heat with the toner carrier or the like, which is a problem when the layer thickness regulating member is provided.

[Brief description of the drawings]

FIG. 1 is a schematic side sectional view of an example of a developing device according to the present invention.

FIG. 2 is a schematic side sectional view of another example of the developing device according to the present invention.

FIG. 3 is a view showing an arrangement relationship between a developer carrier and a toner carrier of the developing device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier 5 Developing device 52 Developing container 53 Toner carrier 55 Developer carrier

Claims (5)

[Claims] A developing container disposed near an image carrier capable of forming an electrostatic latent image and containing a two-component developer comprising a magnetic carrier and a non-magnetic toner therein; A conductive and resilient toner carrier disposed at a predetermined bias and having a predetermined bias applied thereto, and a magnetic field generating means disposed close to or in contact with the toner carrier and disposed inside or itself. An electroconductive developer carrier to which a predetermined bias is applied, and rotating the developer carrier and the toner carrier so that the developer is magnetically generated on the developer carrier by the magnetic field generating means. A brush is formed, and the brush of the brush is brought into contact with the toner carrier to transfer the toner in the developer brush onto the toner carrier to form a thin toner layer. The statue A developing device for developing an electrostatic latent image on an image carrier by contacting the carrier with the carrier. 2. The developer carrier has a length substantially equal to or longer than an effective electrostatic latent image forming width of the image carrier, and the toner carrier has a length equal to the length of the developer carrier. 2. The developing device according to claim 1, wherein the developing device has a longer length toward both ends around the center. 3. The developing device according to claim 1, wherein said developer carrier is provided below said toner carrier. 4. The method according to claim 1, wherein after the development process is completed, the level of the potential difference between the toner carrier and the developer carrier is temporarily reversed to collect the toner on the toner carrier to the developer carrier. The developing device according to claim 1. 5. The developing device according to claim 5, wherein said developer carrier is at a ground potential.